The mechanisms by which polypeptide hormones and cAMP regulate protein biosynthesis will be studied using established functional lines of rat pituitary tumor cells (GH3). The regulation of prolactin and growth hormone biosynthesis by thyrotropin-releasing hormone (TRH) and other hormones, and by cyclic AMP derivatives will be further defined, using specific DNA probes complementary to prolactin and growth hormone mRNAs. The relationship of cell growth to regulation of prolactin gene expression will be evaluated. The site(s) at which TRH and other hormones act to increase intracellular levels of prolactin mRNA will be defined to distinguish between regulation of the levels of transcription, mRNA processing or transport, mRNA catabolism, or translation. This year emphasis will be placed upon: (1) directly measuring the mRNA half-lifes of prolactin and growth hormone mRNAs; (2) directly proving that nuclear species function as precursors of the mature mRNAs; (3) establishing the function and structure of the 1700, 1800 nucleotide species; and finally, (4) initiating studies on expression of the purified prolactin and growth hormone genomic clones.